Why is precise dating important? After all, "baby comes when ready".
This may indeed be so but is not always the case.
When there is an apparent prolongation of a pregnancy, it is too late to verify the dates at the end of pregnancy. An ultrasound scan cannot accurately estimate the gestation if it is performed beyond the second trimester. Such a situation makes the decision of whether to intervene or not very difficult. A post-term pregnancy may be a risk situation, in some circumstances. Having precise dates goes a long way in helping to make the right decisions.
Another situation is when there is a factor that may necessitate premature delivery. The decision in such a situation hinges on knowing the gestation precisely, because fetal survival outside the womb is at stake. If the dates are erroneous and the pregnancy wrongly believed to be more advanced than it actually is, delivery may have disastrous results. An ultrasound scan at twenty weeks will remove this potential problem.
There are a few other scenarios where dating by an early scan comes in useful.
Why is it essential for everybody to be scanned? Can the test not be confined to those "at risk"?
The whole essence of screening is that the test is available to everybody.
Experience shows that problems are usually identified mostly among those where they are least expected, where there is no apparent risk factor. If the scan was offered to only those who are regarded to be at risk, most problems such as fetal abnormalities will be missed.
It should be emphasized here that the vast majority (over 85 per cent) of scanned pregnancies are found to be perfectly normal. However, absence of a detectable problem does not imply wasted effort or resources as it allows for provision of appropriate minimal intervention antenatal care. Nor should one ignore the bonding engendered by this test. Most mothers find the experience positively uplifting.
Does the expectant mother have a choice regarding having the scan?
Of course she has. Like any other antenatal test, the ultrasound scan is voluntary. It is, however, imperative that care-givers ensure that any mother who declines the test is well informed and is not making this decision based on patchy information and half-truths.
What is meant by a "targets scan"?
In some cases, there is an identifiable risk factor for specific fetal abnormalities. This may be in cases of
In others, the earlier blood tests such as the Down's syndrome screening test (also known as the "triple test" or "double test") may have given results that show an increased likelihood of presence of abnormalities. A component of this test may also indicate increased likelihood of neural tube defects such as spina bifida.
In all such cases, the scan is targeted to look very closely for specific potential abnormalities and confirm or rule them out. As a general rule, scans in the older mother (i.e. those in their late thirties or their forties) will be "targeted" because of increased incidence of fetal abnormalities in this age group.